Absolute Value in BGE
This can be done by having two integer properties. One called SpeedRaw and another called SpeedCorrected - the names really do not matter, you will be fine as long as you know which is which.

You simply need to check if SpeedRaw is negative. If it is, it will assign SpeedCorrected the value of SpeedRaw *-1. If SpeedRaw is positive, SpeedCorrected will simply be the same as SpeedRaw.



The end result works as follows:



This also works for float values, however the second property sensor needs to detect when SpeedRaw is greater than 0, not -1.